The present invention relates to laminates, and more particularly to thin film laminates. Thin film laminates are useful in many applications, particularly where the properties of one layer of the laminate complement the properties of another layer, providing the laminate with a combination of properties that cannot be obtained in a single layer film.
Photovoltaic (PV) devices are characterized by the efficiency with which they can convert incident solar power to useful electric power. Devices utilizing crystalline or amorphous silicon have achieved efficiencies of 23% or greater. However, efficient crystalline-based devices are difficult and expensive to produce. In order to produce low-cost power, a solar cell must operate at high efficiency.
A number of techniques have been proposed for increasing the efficiency and effectiveness of PV modules. One approach is to enhance light reflection by a protective back sheet for the solar cell.
Japanese Published Patent Application No. 62-10127 suggests providing a solar cell module with a reflective back cover sheet in the form of a laminate comprising a polyester base layer and a light-reflecting aluminum coating, with the back cover sheet having a plurality of V-shaped grooves that provide angular light reflecting facets. The cells are spaced from one another in front of the back sheet, so that incident light passing through the front cover sheet and between the cells is reflected by the back cover sheet back to the transparent front cover sheet.
Gonsiorawski, in U.S. Published Patent Application No. 2004-0035460, teaches production of photovoltaic modules with a back cover sheet of an ionomer/nylon alloy embossed with V-shaped grooves running in at least two directions and coated with a light reflecting medium.
Even though the inventions mentioned above provide a significant power boost, the techniques described are time consuming and expensive. The textured material is produced in several steps. First, the film that serves as the substrate is manufactured as a continuous or extended web having flat front and back surfaces, and that continuous web is then wound onto a roll for subsequent processing. The subsequent processing comprises first embossing the film so as to form V-shaped grooves on one side, and then metallizing the grooved surface of the film. The film is heated so that, as it passes between the two rollers, it is soft enough to be shaped by the ridges on the embossing roller. After formation of grooves, the plastic film is subjected to a metallizing process wherein an adherent metal film is formed. The metallized film is wound on a roll for subsequent use as a light reflector means. Such a process is described in Kardauskas, U.S. Pat. No. 5,994,641.
Laminates described in Kernander et al., U.S. Pat. No. 6,319,596, have at least one outer layer of polyvinyl fluoride and a mid-layer. Such laminates have been used effectively in the preparation of photovoltaic cells, solar panels and circuit boards. Polyester films have been used effectively as a mid-layer in these laminates, alone or in combination with other mid-layers. Such laminates having a polyester mid-layer have been found to be particularly satisfactory for a variety of applications. However, with long-term use, the polyester film or other mid-layer can undergo some degree of degradation. Such degradation typically results in a yellowing of the film, which, while not detrimental to its performance characteristics, is aesthetically undesirable.
A need accordingly remains for a laminate that exhibits high dielectric strength, provides effective protection for the current generated in a photovoltaic module, and which remains aesthetically satisfactory over extended use. In addition, a need exists for a protective laminate, the components of which maximize the pathways for gases formed during the lamination process to escape. Particularly when such laminates are used for backing on photovoltaic cells, it is desirable to have a protective structure that will not interfere with the functioning of the cell, and, if possible, aid in the generation of power.